System and method for performing auto-location of a tire pressure monitoring sensor arranged with a vehicle wheel

ABSTRACT

Auto-location systems and methods of tire pressure monitoring sensor units arranged with a wheel of a vehicle detect a predetermined time (T 1 ) when a wheel phase angle reaches angle of interest using a rim mounted or a tire mounted sensor. The systems and methods transmit a radio frequency message associated with a wheel phase angle indication. The wheel phase angle indication triggers wheel phase and/or speed data such as ABS data at the predetermined time (T 1 ) to be stored. A correlation algorithm is executed to identify the specific location of a wheel based on the wheel phase and/or speed data at the predetermined time (T 1 ). TPM sensor parameters from a tire pressure monitoring sensor unit are assigned to the specific location of the wheel.

PRIORITY

This application is a continuation of U.S. application Ser. No.13/222,653 filed Aug. 31, 2011, entitled “System and method forperforming auto-location of a tire pressure monitoring sensor arrangedwith a vehicle wheel,” which is a continuation-in-part of U.S.application Ser. No. 12/888,247 filed Sep. 22, 2010, entitled “Systemand method for performing auto-location of a wheel in a vehicle usingwheel phase angle information,” which claims priority to ProvisionalApplication No. 61/277,334 filed on Sep. 22, 2009, entitled “Use ofwheel phase angle to perform auto-location in a Tire Pressure MonitoringSystem.” Disclosures of U.S. application Ser. Nos. 13/222,653 and12/888,247 and Provisional Application No. 61/277,334 are incorporatedhere in their entirety.

BACKGROUND

1. Technical Field

This invention relates generally to a system and method for performingauto-location of a wheel in a vehicle and more particularly to a tirepressure monitoring system and method for performing auto-location of atire pressure monitoring sensor arranged with a vehicle wheel usingwheel phase and/or speed data.

2. Related Art

In tire pressure monitoring systems, performing auto-location of a wheelis needed for a number of reasons. Tire pressure monitoring systemsgenerally include a tire pressure monitoring (TPM) sensor in or at eachwheel of a vehicle and a central controller which receives tire pressureinformation from each TPM sensor, to be reported to the driver of thevehicle. Auto-location is the identification of each TPM sensor anddetermination of its position on the vehicle, automatically and withouthuman intervention. Auto-location may be done initially uponinstallation and subsequently in the event of tire rotation orreplacement. Performing auto-location involves determining the identityor serial number of a TPM sensor in each of the wheels in the car. Inpremium vehicles, knowing the identity of the TPM sensor in each wheelallows a pressure by position display to be implemented and shown to thedriver. In basic vehicles with different placard tire pressures forfront and rear axles, it is desirable to know TPM sensor identities andpositions in order to check pressure against a correct threshold for anapplicable axle.

SUMMARY

The present embodiments are directed to auto-location systems andmethods in which wheel phase and/or speed data is correlated with aspecific wheel to determine a location of a TPM sensor and facilitateidentification of the TPM sensor arranged with the specific wheel on avehicle. The present embodiments determine the wheel location in orderto determine the location of a TPM sensor arranged with the wheel. Inthe present embodiments, the auto-location of a wheel indicatesauto-location of the TPM sensor arranged with the wheel so thatparameters from the TPM sensor may be assigned to the wheel. The wheelphase and/or speed data can be processed and correlated with wheel phaseangle information or a wheel phase angle indication from a wheel unit.The present systems and methods are particularly well suited for usewith tire pressure monitoring systems that use rim mounted sensors thatcan deduce the instantaneous wheel angle using shock sensors.Alternatively, or additionally, the present systems and methods can alsobe practiced in a tire pressure monitoring system that uses a rimmounted sensor which is able to deduce the instantaneous wheel angleusing accelerometers. The present systems and methods are also wellsuited for use with tire pressure monitoring systems that use tiremounted sensors that deduce the instantaneous wheel angle. This methodof auto-location is not limited to the use of accelerometric devices.For example, periodic signals from which phase information can bededuced may also be used. Devices such as Hall effect sensors or sensorswhich respond to road strike may be used to deduce the phaseinformation.

Advantageously, most vehicles employ antilock brake systems (“ABS”). TheABS allows independent wheel speeds to be monitored in near real-time.In one embodiment, the wheel phase and/or speed data includes or isbased on the ABS data. Correlation between ABS data and other data fromTPM sensors can be used to locate wheel positions where the TPM sensorsare arranged. ABS sensors provide the ABS data and may be associatedwith one or more wheels. As one example, ABS sensors are associated witheach wheel of a vehicle, or with selected wheels of the vehicle. Thewheel phase and/or speed data is not limited to the ABS data. A sensor,a device, a system, or a mechanism that may provide wheel phase and/orspeed data directly or in various forms may be used in addition to, orinstead of antilock brake systems.

In one embodiment, the identification of the wheel location, therebyidentifying the location of the TPM sensor, may require snapshots ofinformation at a one-measurement point during rotation of a wheel, wherea snapshot is a capture of information from a short duration of acontinuous stream of information. A radio frequency (RF) transmissionidentifying the one-measurement point is transmitted from a wheel unitand correlated to the ABS data at the one-measurement point using astatistical processing method. A historic trace of the ABS data at theone-measurement point is correlated to a specific wheel location.

By way of one example, one embodiment of a wheel auto-location methodincludes (i) arranging a wheel unit to be associated with a wheel of thevehicle, the wheel unit comprising a TPM sensor and a wheel phase anglesensor and the wheel unit transmitting TPM sensor parameters; and (ii)arranging an ABS sensor to be associated with each wheel of the vehicle,the ABS sensor producing ABS data indicative of the wheel phase angle.The ABS sensor provides wheel phase and/or speed data in thisembodiment; however, the wheel phase and/or speed data is not limited toABS data. In this embodiment, the wheel auto-location method detects afirst time (T1) reaching a particular wheel angle of interest andtransmits a radio frequency (RF) message at a second time (T2). A wheelphase angle at the second time (T2) may not be measured. The wheelauto-location method then triggers a phase correlation data storageevent based on wheel phase angle indication. In response to the wheelphase angle indication, the phase correlation data storage event istriggered and the current contents of a rolling window of the ABS datais captured. The rolling window of the ABS data is continuouslymaintained and the captured current content of the rolling window isstored in storage. After a substantial amount of the ABS data iscaptured, an auto-location algorithm is executed and applied to thestored ABS data in order to identify a specific location of the wheel.

The phase correlation data storage event trigger is implemented withvarious embodiments of the wheel phase angle indication. In oneembodiment, the wheel phase angle indication includes a function code,or a status code contained in the RF message. Upon receipt of such RFmessage, the phase correlation data storage event is triggered and thecurrent content of the rolling window of the ABS data is captured. Inanother embodiment, the RF message uses at least a portion of bits of atemperature data field of the RF message as the wheel phase angleindication. The temperature data bits are recognized and the currentcontent of relevant ABS data is captured. Further in another embodiment,interframe spacings of a series of RF messages operate as the wheelphase angle indication. The interframe spacings are recognized and therelevant ABS data is captured.

Another embodiment of the present invention includes a wheelauto-location system that determines a location of a TPM sensor. Thesystem includes a wheel unit to be associated with a wheel of thevehicle. The wheel unit includes the TPM sensor that measures tirepressure of the wheel and a wheel phase angle sensor that detects afirst time (T1) when a wheel phase angle reaches a particular angle ofinterest. The wheel unit transmits an RF message at the second time(T2). The RF message includes an identification of the TPM sensor andmeasured tire parameters such as tire pressure. The RF message may notinclude an actual phase angle. Alternatively, or additionally, the RFmessage includes position or location information of the TPM sensor suchas left side or right side of a vehicle.

In this embodiment, the wheel auto-location system further may includeor may work in cooperation with an antilock brake system (“ABS”) sensorassociated with each wheel of the vehicle and operable to provide ABSdata indicative of the wheel phase angle. The ABS data may be used aswheel phase and/or speed data, but other data that represents wheelphase and/or speed is available. The wheel auto-location system furtherincludes or operates in conjunction with an Electronic Control Unit(“ECU”) in communication with the wheel unit and the ABS sensor. ABSdata from the ABS sensors are available to other components of thevehicle such as the wheel auto-location system and the ECU. The ECU maybe operable to execute instructions of calculating the first time (T1)based on a predetermined time delay, determining the ABS data at thecalculated first time (T1) and identifying a location of the wheel whoseABS data matches with a predetermined criterion.

In one embodiment, the predetermined criterion is based on a historictrace of the ABS data at the first time (T1). The predeterminedcriterion is also based on a statistically significant value of the ABSdata. For example, the ECU correlates the location of the wheel havingthe TPM sensor with the location of the ABS sensor whose historic traceshows a lowest standard deviation of ABS tooth count values at the firsttime (T1) over time. Alternatively, or additionally, the ECU correlatesthe location of the wheel having the TPM sensor with the location of theABS sensor whose historic trace shows the most consistent ABS toothcount values at the first time (T1) over time. Alternatively, oradditionally, the ECU correlates the location of the wheel having theTPM sensor with the location of the ABS sensor whose historic traceshows a statistically significant trend in ABS tooth count values at thefirst time (T1) over time.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part ofthe specification and in which like numerals designate like parts,illustrate embodiments of the present invention and together with thedescription, serve to explain the principles of the invention. In thedrawings:

FIG. 1 illustrates one embodiment of a tire pressure monitoring system;

FIG. 2 illustrates one embodiment of a wheel unit for use with the tirepressure monitoring system.

FIG. 3A illustrate a wheel phase angle as a function of thegravitational force, i.e., acceleration and FIG. 3B illustrates phasevarying signals from different sensors.

FIG. 4 illustrates one embodiment of correlation between wheel phaseangle information from the wheel unit and ABS data.

FIG. 5 is a flow chart illustrating one embodiment of a method forperforming auto-location of a wheel using wheel phase angle informationat the wheel unit.

FIG. 6 is a flow chart further illustrating the method for performingauto-location of the wheel at an Electronic Control Unit (“ECU”).

FIG. 7 is a flow chart illustrating another embodiment of the method forperforming auto-location of the wheel using wheel phase angleinformation.

FIG. 8 is a flow chart illustrating another embodiment of the method forperforming auto-location of the wheel using wheel phase angleinformation.

FIG. 9 is a flow chart illustrating another embodiment of the method forperforming auto-location of the wheel using wheel phase angleinformation.

FIG. 10A illustrates correlation between ABS data and a one-measurementpoint during a rotation of a wheel and FIG. 10B illustrates storage ofthe ABS data at the one-measurement point.

FIGS. 11A-11D illustrate various embodiments of a phase correlation datastorage event trigger based on various wheel phase angle indications.

FIG. 12 is a flow chart illustrating one embodiment of an auto-locationmethod based on the ABS data at the one-measurement point.

FIG. 13 illustrates one embodiment of ABS tooth count values for fourwheels with respect to RF transmissions from a left rear wheel unit.

FIG. 14 is a graph illustrating ABS tooth count values of FIG. 13.

FIG. 15A illustrates one embodiment of a standard deviation of ABSsensor tooth count values with respect to RF transmissions from a leftrear wheel unit, and FIG. 15B illustrates one embodiment of a trend ofABS sensor tooth count values with respect to RF transmissions from aleft rear wheel unit.

FIG. 16 illustrates one example of a standard deviation of ABS toothcount values for four wheels with respect to RF transmissions from leftfront, right front, left rear and right rear wheels.

FIG. 17 is a flowchart illustrating one embodiment of an auto-locationalgorithm.

FIG. 18 is a flowchart illustrating another embodiment of anauto-location algorithm where not every wheel has an associated ABSsensor.

DETAILED DESCRIPTION

The present invention is directed to systems and methods in which ameasurement from a wheel is combined or correlated with wheel phaseand/or speed data such as antilock brake system (ABS) data to allowidentification of the TPM sensors to a specific location on a vehicle.In accordance with various embodiments of the present invention, a tirepressure monitoring system comprises wheel rim or tire mounted TPMsensors, typically four, and an Electronic Control unit (ECU) thatreceives signals from the TPM sensors. In addition, the system employsdata presented to the ECU from the Anti-lock Brake System (ABS).

In accordance with various embodiments of the present invention, theidentification of the TPM sensors may require snapshots of informationat one-measurement point during a rotation of a wheel, where a snapshotis a capture of information from a short duration of a continuous streamof information. The ECU holds a rolling window of ABS data for allwheels or selected wheels associated with ABS sensors. When a radiofrequency (RF) data frame is received, the ECU uses the RF data frame tostore and determine relevant ABS data from the rolling window of the ABSdata. An auto-location algorithm is applied to stored ABS data toidentify a specific location of a wheel where a TPM sensor is arranged.The auto-location algorithm may analyze a historic trace of the ABS dataand determines a standard deviation of ABS tooth count values withrespect to each wheel of a vehicle. Alternatively, or additionally, theauto-location algorithm may analyze a statistically significant trend ofthe ABS data.

FIG. 1 illustrates a tire pressure monitoring system 100 according to afirst embodiment of the present invention. The system 100 is arranged ina standard vehicle 1 having four wheels. Four wheels include a leftfront wheel (LF), a right front wheel (RF), a left rear wheel (LR) and aright rear wheel (RR). In another embodiment, the system 100 may bearranged in any other vehicle having a different number of wheels. Thesystem 100 includes wheel units 101, 102, 103 and 104 that areassociated with each wheel of the vehicle 1.

The system 100 further includes four antilock brake system (ABS) sensors201, 202, 203 and 204. In this embodiment, ABS sensors 201, 202, 203,204 are also associated with each wheel of the vehicle 1. Accordingly,each wheel is assigned with one of the wheel units 101, 102, 103 and 104and one of ABS sensors 201, 202, 203 and 204. In another embodiment, ABSsensors 201, 202, 203, 204 may not be associated with all four wheels.Fewer numbers of ABS sensors may be present in a structure of a vehiclesuch as a single axle and associated with a few selected wheels.

The system 100 also includes an Electronic Control Unit (ECU) 300 and areceiver 400. The ECU 300 is coupled to the ABS sensors 201, 202, 203,204 via a communication bus such as a Controller Area Network (CAN) busand receives ABS data from the ABS sensors 201, 202, 203, 204. The ECU300 includes a processor 302 and storage 304. The ECU 300 operates tostore received ABS data in the storage 304 to provide a historic ABStrace. The ECU 300 may be implemented by any suitable means, for examplea microprocessor, microcontroller, an Application Specific IntegratedCircuit (ASIC), or other suitable data processing device programmed toperform the functions described herein. Further, the ECU 300 maycommunicate with other vehicle components using any other suitabledevice, either wire line or wireless. The CAN bus is an exemplaryimplementation of data communication among components of the vehicle.The ECU 300 stores computer program code. In one embodiment, the ECU 300executes the computer program including instructions of calculating afirst time (T1) based on a predetermined time delay (T2−T1), storing ABSdata indicative of a wheel phase angle based on a phase correlation datastorage event trigger and determining the ABS data at the first time(T1), and correlating a location of the wheel with a location of the ABSsensor based on a historic trace of the ABS data at the first time (T1).

The ECU 300 also receives data from the wheel units 101,102, 103 and 104via the receiver 400. For example, the wheel units 101, 102, 103 and 104transmit radio frequency or other wireless communications conveying dataand other information to the ECU 300. The respective wheel units includea suitable radio transmission circuit and the ECU 300 includes asuitable radio reception circuit for radio communication. Further, theradio circuits may use an agreed upon transmission and reception formatand data encoding technique. The ECU 300 operates to correlate the datareceived from the wheel units 101, 102, 103 and 104 with the ABS data inorder to perform auto-location, as will be discussed in detail below.

Referring to FIG. 2, the structure of the wheel unit 101 is illustratedin more detail. The wheel units 102-104 may incorporate the samestructure as that of the wheel unit 101. As shown in FIG. 2, the wheelunit 101 includes a microcontroller 202, a battery 204, a transpondercoil 206, a sensor interface 207, a pressure sensor 208, a wheel phaseangle sensor 212, a transmitter 214 and an antenna 216. In otherembodiments, the wheel unit 101 may have a different structure from thestructure illustrated in FIG. 2. The microcontroller 202 is coupled tothe sensor interface 207. The sensor interface 207 is coupled to thewheel phase angle sensor 212. In one embodiment, the wheel phase anglesensor 212 measures a wheel phase angle at multiple different times. Thewheel phase angle sensor 212 provides measurements to the sensorinterface 207. Alternatively, or additionally, the wheel phase anglesensor 212 provides other value or information indicative of wheel phaseangle measurements. The sensor interface 207 receives the measurementsof the wheel phase angle sensor 212 in the form of an electrical outputsignal. The sensor interface 207 receives the electrical output signaland amplifies and filters the signal. The sensor interface 207 sends theprocessed signal to an analog to digital converter (not shown) in orderto convert the signal into a digital signal. The microcontroller 202receives the digital form of the output signal from the wheel phaseangle sensor 212 for processing.

In the illustrated embodiment, the pressure sensor 208 detects thepneumatic air pressure of the tire with which the wheel unit 101 isassociated. In alternative embodiments, the pressure sensor 208 may besupplemented with or replaced by a temperature sensor or other devicesfor detecting tire data. An indication of the tire pressure data is sentto the microcontroller 202 via the analog-to-digital converter (notshown).

The battery 204 is a power source of the wheel unit 101. The transpondercoil 206 detects external activation of the transponder by a signalapplied by a remote exciter and may modulate a signal to communicatedata to a remote detector from the wheel unit 101. The wheel unit 101provides data including tire pressure from the pressure sensor 208 andthe wheel phase angle information from the wheel phase angle sensor 212through the transmitter 214 and the antenna 216 to the ECU 300 (see FIG.1).

Upon rotation of a wheel, the wheel phase angle sensor 212 operates tomeasure a wheel phase angle. The wheel phase angle measurements may nothave to be against an absolute reference. The reference may bearbitrarily selected based on accuracy capability and ease ofimplementation. In other words, the phase measurements do not have to bemeasured from a top of wheel, or road striking point. In thisembodiment, the key piece of information may be a phase difference, or aphase delta of the wheel, and therefore, the requirement is that twodifferent phase angles are measured relative to the same angle.Alternatively, or additionally, in another embodiment, the key piece ofinformation may include a one-measurement point during a rotation of awheel.

The wheel phase angle sensor 212 may be mounted on a rim of the wheel,or a tire mounted sensor. Alternatively, or additionally, the wheelphase angle sensor 212 may be arranged on any suitable locationassociated with a wheel. In one embodiment, the wheel phase angle 212includes a rotation sensor. For example, the rotation sensor may be apiezoelectric rotation sensor which measures a wheel phase angle basedon the gravitational force. Specifically, as the wheel rotates, thegravitational force causes a sensing element of the rotation sensor toexperience different forces which results in a different output signalrepresenting a wheel phase angle or wheel angular position. In that way,the rotation sensor produces an output signal indicating a wheel phaseangle at a predetermined time. The output signal of the rotation sensormay have different amplitude and/or different polarity depending on thewheel phase angle. For instance, the rotation sensor produces the outputsignal having amplitude M at 0 degree and having the amplitude −M at 180degree. Alternatively, or additionally, any conventional rotation sensormay be used as the wheel phase angle sensor 212.

In another embodiment, the wheel phase angle sensor 212 comprises ashock sensor of the type that produces an electrical signal in responseto acceleration. The electrical signal is indicative of, or typicallyproportional to, the experienced change in acceleration. Alternatively,the wheel phase angle sensor 212 may each comprise an accelerometer or amicro-electromechanical systems (MEMS) sensor. The main differencebetween an accelerometer and a shock sensor is that the output signalfrom a shock sensor is related to a change of force applied to the shocksensor, whereas the output signal from an accelerometer is proportionalto the absolute force applied. Shock sensors may be implemented, forexample, with shock sensors discussed in commonly owned U.S. Pat. No.7,362,218, issued Apr. 22, 2008 and entitled Motion Detection Using AShock Sensor In A Remote Tire Pressure Monitor System and commonly ownedU.S. Pat. No. 7,367,227, issued May 6, 2008 and entitled DeterminationOf Wheel Sensor Position Using Shock Sensors And A Wireless Solution,the disclosures of which are incorporated here in its entirety.Accelerometer sensors may be implemented, for example, with sensorsdiscussed in commonly owned U.S. Pat. No. 7,010,968, issued Mar. 14,2006 and entitled Determination Of Wheel Sensor Position Using AWireless Solution, the disclosure of which is incorporated here in itsentirety.

In the embodiment where shock sensors or accelerometers are used as thewheel phase angle sensor 212, FIG. 3A is a graph illustrating a wheelphase angle or a wheel angular position as a function of thegravitational force or acceleration. In the illustrated embodiment, thewheel rotates counter clockwise, and acceleration along the z axis 304leads acceleration along the x axis by approximately 90 degrees. Theoutput signal is a sinusoid with a period equal to one revolution of thewheel. The magnitude of the output signal is a voltage proportional tothe change in acceleration or acceleration experienced by the wheelphase angle sensor 212 such as the shock sensors or accelerometers asthey rotate. The graph as shown in FIG. 3A is by way of example, and theactual acceleration experienced in a moving wheel may be different fromthe amount illustrated in FIG. 3A.

FIG. 3B(a) illustrates phase varying signals output from the wheel phaseangle sensor 212 which may be a shock sensor or an accelerometer. FIG.3B(b) illustrates phase varying signals output from the wheel phaseangle sensor 212 which may be a Hall effect sensor, or a road strikingsensor. The phase varying signals illustrated in FIG. 3B (a) and (b) areinput to the microcontroller 202. The microcontroller 202 recognizes arepeated pattern in the phase varying signals and determines onerotation of the wheel. Then, the microcontroller 202 determines how farthrough the one rotation of the wheel it is at the first time (T1) andthe second time (T2) and determines a first phase angle (P1) and asecond phase angle (P2). Assuming that the phase-varying signal does notchange its characteristics between the first time (T1) and the secondtime (T2), the first phase angle (P1) and the second phase angle (P2)will be relative to each other, and can be used as auto-location data.

Referring back to FIG. 2, the sensor interface 207 is configured toprovide the necessary control signals and detect the electrical signalsfrom the wheel phase angle sensor 212 such as the shock sensor. Asdiscussed above, the shock sensor detects change in acceleration toproduce an output in the form of an electrical charge output signal. Theoutput signal is typically in the order of 1 mV/g. Preferably, if thewheel phase angle sensor 212 includes more than one shock sensor, shocksensors can share the same interface 207 via multiplexing.

Through the sensor interface 207, the microcontroller 202 receivesoutput signals representing wheel phase angle from the wheel phase anglesensor 212. The microcontroller 202 may include, for example a memoryfor data storage and a data processing unit. The microcontroller 202stores a received wheel phase angle, or data related thereto, for alater transmission to the ECU 300. The microcontroller 202 may nottransmit every time the output signal has been received. In oneembodiment, the microcontroller 202 calculates and determines adifference in two wheel phase angles measured by the wheel phase anglesensor 212. For instance, the microcontroller 202 subtracts a firstwheel phase angle measured at a first time (T1) from a second wheelphase measured at a second time (T2). In another embodiment, themicrocontroller 202 determines the second time (T2) based on apredetermined known time delay (T2−T1). For instance, themicrocontroller 202 may consider the first time (T1) as theone-measurement point of a wheel phase angle during the rotation of awheel and the second time (T2) as a data transmission point of a radiofrequency message as described below. The microcontroller 202 mayinclude a clock or time base, or other circuit or module for measuringtime increments and operating at specified times or during specifiedtime durations.

The microcontroller 202 encodes and transmits a radio frequency messagevia the transmitter 214 and the antenna 216. The radio frequency messageincludes, among other things, tire pressure information, an identifierof the wheel unit 101, and wheel phase angle information. The wheelphase angle information may include actual wheel phase angles measuredat different times. In another embodiment, the wheel phase angleinformation may include wheel phase angle measured at a transmissiontime, such as the second time (T2), and a difference in wheel phaseangle measured at two different times. Alternatively, the wheel phaseangle information may include only the difference in wheel phase angles.

In another embodiment, the wheel phase angle information may include noactual wheel phase angle. Instead, the wheel phase angle informationincludes a wheel phase angle indication. As one example, the wheel phaseangle indication may include a predefined function code which willtrigger a phase correlation data storage event. The wheel phase angleindication may be implemented by establishing predetermined data valuesor patterns such as by setting a bit which is normally unused in a RFmessage structure (see FIG. 11A). Alternatively, or additionally, thewheel phase angle indication may be implemented with a most significantbit, which is normally set to zero (see FIG. 11B). Additionally, thephase wheel angle indication may also include a predetermined timedelay, such as T2−T1, or any other information indicative of a wheelphase angle (e.g., a pseudo-random number).

Referring again back to FIG. 1, the ECU 300 receives the radio frequencymessage from the wheel unit 201. The ECU 300 stores the radio frequencymessage, or data contained in the radio frequency message. Such data maybe stored in the storage 304 which is a suitable data store such as amemory device. Also, the ECU 300 extracts the tire pressure, theidentifier, and the wheel phase angle information from the radiofrequency message. The ECU 300 correlates the wheel phase angleinformation with the ABS data from the ABS sensors 201, 202, 203, 204.In one embodiment, the ECU 300 analyzes the ABS data and determines awheel phase angle or a wheel phase angle difference which is indicatedby and corresponds to the ABS data. The ECU 300 compares the wheel phaseangle information from the wheel unit 101 with the wheel phase angle orthe wheel phase angle difference of the ABS data in order to determinethe closest match. Upon finding the closest match, the ECU 300 assignsthe identifier sent from the wheel unit 101 to a wheel whose ABS datamost closely matches with the wheel phase angle information from thewheel units 101, 102, 103, 104.

In another embodiment, the ECU 300 analyzes the ABS data and determineswhether the ABS data maintains a consistent value or a statisticallysignificant trend at a predetermined time (e.g., T1). Alternatively, oradditionally, the ECU 300 analyzes the ABS data and determines whetherthe ABS data shows a lowest standard deviation for a particular wheellocation. By using this statistical correlation method, as will bedescribed in detail below, the ECU assigns the identifier sent from thewheel unit 101 to a wheel whose ABS data is the most consistent or showsthe lowest deviation, or shows the a statistically significant trend.

Referring to FIG. 4, correlation of the wheel phase angle informationfrom the wheel unit 101, 102, 103, 104 with the ABS data is furtherexplained. In one embodiment, the wheel phase angle sensor 212 measuresa wheel phase angle multiple times. In another embodiment, the wheelphase angle sensor 212 measures a wheel phase angle at theone-measurement point (e.g., T1 in FIG. 4) and does not measure thewheel phase angle at a different time (e.g., T2 in FIG. 4). In thisembodiment, the wheel phase angle sensor 212 measures a first wheelphase angle (P1) at a first time (T1) and waits a predetermined time.The wheel phase angle sensor 212 then transmits a radio frequencymessage at a second time (T2) where T2=T1+Predetermined Time. The methodwith which the time T2−T1 is predetermined will be discussed later.Alternatively, the wheel phase angle sensor 212 measures the first wheelphase angle (P1) and detects the first time (T1) when the wheel phaseangle reaches the first wheel phase angle (P1), which will be furtherdescribed later. In this embodiment, the wheel units 101, 102, 103, 104may be pre-programmed to recognize this Predetermined Time. For example,in a tire mounted TPM sensor the act of “striking” the ground providesan indication that the tire sensor has completed a revolution, relativeto a previous “strike.” If the TPM sensor reports the time since thelast strike, then the phase of the wheel can be deduced. It may also bedesirable, although not essential, that the period of the wheelrevolution may also be sent.

In one embodiment, the Predetermined Time (T2−T1) may be fixed andselected to ensure multiple wheel rotations between the first time (T1)and the second time (T2). In case the difference in wheel speed betweenvehicle wheels may be small, setting the value of the Predetermined Time(T2−T1) to cover multiple wheel rotations may improve accuracy of theauto-location. Accordingly, a tire pressure monitoring system accordingto this embodiment may sufficiently comply with accuracy requirements.Alternatively, in another embodiment, a period between the first timeand the second time (T1, T2) may be variable, whereas a phase angledifference or a phase delta may be fixed. This embodiment will befurther explained in detail below.

As discussed in connection with FIG. 2 above, the microcontroller 202calculates and determines a wheel phase angle difference (PD) bysubtracting the second wheel phase angle (P2) from the first wheel phaseangle (P1). The wheel phase angle difference (PD) may range between 0degree and 360 degree. In this embodiment, the wheel units 101, 102,103, 104 may transmit a radio frequency message including the wheelphase angle difference to the ECU 300. The wheel units 101, 102, 103,104 may transmit the radio frequency message at a time that the wheelphase angle difference (PD) is obtained, i.e., the second time (T2).Because the wheel units 101, 102, 103, 104 provide the wheel phase angledifference (PD), the ECU 300 may reduce the burden of calculating thewheel phase angle difference. Tire pressure monitoring systems aretime-critical applications, and additional time to process thecalculation of the wheel phase angle difference (PD) may introduceuncertainty and increase inaccuracy.

As shown in FIG. 1, the ECU 300 periodically receives ABS data from theABS sensors 201, 202, 203, 204. Additionally, the vehicle may include anElectronic Stability Control (ESC) system which may be the source ofother inputs, such as steering angle, vehicle yaw, etc. to the ABSsystem information to help control vehicle progress through curves inthe road. For instance, the ECU 300 receives the ABS data every 40 ms.As shown in FIG. 4, a rolling window of ABS data is stored, running fromthe present point to a point in the past. In this embodiment, therolling window of the ABS data is stored for each wheel throughout theentire drive. The rolling window of the ABS data is variable and largeenough to contain the first time (T1). The stored ABS data provides ahistoric ABS trace between the first time (T1) and the second time (T2).The ABS data includes information that is used to measure a phasethrough which the wheel has rotated. In one embodiment, the ABS data mayinclude a number of ABS teeth that pass through the ABS sensors 201,202, 203, 204 during a predetermined period of time. Only as oneexample, 48 teeth pass through the ABS sensor 210, which indicatescompletion of a full cycle. The ABS data for the number of counts may bedivided by the number of teeth per wheel which is constant. Theremainder of the number of counts divided by the number of teeth givesan estimate of wheel angle change over any given period. Using the aboveexample of 48 teeth, 48/48=1 and the remainder is zero. Accordingly, theECU 300 determines that there is no wheel phase angle change.

As shown in FIG. 4, the first time (T1) and the second time (T2) mayserve as time points at which correlation of wheel phase angles (P1, P2)with ABS data shall occur. The time delay or the time period between thefirst time (T1) and the second time (T2) may be predetermined in orderto ensure generation of effective phase angle data and ABS data thatresult in accurate auto-location. The time delay or the time periodbetween the first time (T1) and the second time (T2) may be known to theECU 300 and the wheel units 101-104 such that the first time (T1), thesecond time (T2), the first phase angle (P1), etc. may be latercalculated and determined. Alternatively, in another embodiment, thetime period between the first time (T1) and the second time (T2) may bevariable.

Referring to FIGS. 5-8, a method for performing auto-location of a wheelusing wheel phase angle information is explained in detail. FIG. 5 is aflow chart illustrating one embodiment of a method for performingauto-location of a wheel using wheel phase angle information. Inparticular, FIG. 5 shows operations at the wheel unit 101 forconvenience. The operations at the wheel unit 101 may be equallyapplicable to the wheel units 102, 103, 104. In the embodimentillustrated in FIG. 5, the time period between the first time (T1) andthe second time (T2) is pre-determined, whereas a phase angle differencebetween the first phase angle (P1) and the second phase angle (P2) isvariable.

As shown in FIG. 5, at the wheel unit 101, the first wheel phase angle(P1) is measured at the first time (T1) and the second wheel phase angle(P2) is measured at the second time (T2) after passage of thepredetermined time (Step 502). At the wheel unit 101, the wheel phaseangle difference (PD) is calculated by subtracting P1 from P2 (Step504). The microcontroller 202 generates the radio frequency messageincluding tire pressure, the identifier of the TPM sensor 208, and thewheel phase angle information. The radio frequency message istransmitted via the transmitter 214 and the antenna 216 (Step 506). Theradio frequency message is transmitted a plurality of times (e.g., 5times or 8 times) to ensure that the ECU 300 receives the message,considering clashing and path loss. Thus, interframe spacing may beintroduced to avoid clashing, which occurs when two transmitterstransmit at the same time so as to be indistinguishable to the receiver.(Step 520). The same wheel phase angle information is duplicated in eachframe 1 to 8. If the first frame of data is not received, then the ECU300 must be able to calculate the time at which frame 1 was transmittedin order for the wheel phase angle data to be accurate (Step 520).Therefore, the transmitted frames which contain the wheel phase angleinformation need a predetermined interframe spacing known to the ECU300. The frames may be numbered 1 through 8, or alternatively, the framenumber information could be deduced by the ECU from the interframespacing.

In one embodiment, the wheel phase angle information includes the firstwheel phase angle (P1) and the second wheel phase angle (P2). The wheelunit transmits the first and the second wheel angles (P1 and P2) at thesecond time (T2) (Step 508). In another embodiment, the wheel phaseangle information includes the second wheel phase angle (P2) and thewheel phase angle difference (PD) which is transmitted at the secondtime (T2) (Step 510). In further another embodiment, the wheel phaseangle information includes only the wheel phase angle difference (PD)(Step 512).

FIG. 6 is a flow chart illustrating one embodiment of the method forperforming auto-location of the wheel using wheel phase angleinformation at the ECU 300. In the illustrated embodiment, the wheelphase angle difference (PD) is received at the second time (T2) (Step602 and Step 512). Here it is assumed that the ECU 300 has received thefirst frame. The ECU 300 calculates the first time (T1) based on thefixed time delay which is known to the ECU 300 (Step 604). The firsttime (T1) may need calculation to give a reference point at which theABS data will be analyzed. As noted above, the period between the firsttime (T1) and the second time (T2) is set up to ensure that a meaningfulphase angle difference between the measured phase angles can beobtained.

After determining the first time (T1), the ECU 300 is able to calculatea phase angle difference for each ABS data per wheel between T1 and T2(Step 606). Using the example discussed above, 48 teeth of ABS teeththat have passed the period between T1 and T2 may indicate two fullrotations of the wheel and the zero remainder of 48 teeth/24 teethindicates zero phase angle difference. The ECU 300 compares the wheelphase angle difference (PD) against the phase angle difference for eachABS data (Step 608). In other words, the ECU may estimate, byinterpolation of the RF message phase measurement, what the number ofcounts from each ABS sensor would have been and search for a match fromthe ABS data for a wheel unit that has a similar wheel angle. Thepurpose of the correlation is to determine which set of ABS data matcheswith the deduced phase rotation of the wheel phase angle sensor 212.

There are a number of ways to perform the interpolation. For example,linear interpolation based on the assumption that the vehicle speed isrelatively constant may be used. For example, every wheel on the vehiclewill rotate at least 0.1% difference in overall effective circumference.After 60 seconds at 40 kmh (typically 5.5 Hz), the difference in angularrotation of each wheel will likely be 0.001*5.5*60. This equates to ⅓ ofa revolution or 120 degrees. As a result, the ECU 300 assigns theidentifier to a location whose phase angle difference of ABS data mostlyclosely matches to the wheel phase angle difference transmitted from thewheel unit 101.

FIG. 7 is a flow chart illustrating another embodiment of theauto-location method. In the illustrated embodiment, the wheel phaseangle (P2) and the wheel phase angle difference (PD) are received at thesecond time (T2) (Step 702 and Step 510, as shown in FIG. 7. It isassumed that the ECU 300 has received the first frame. The ECU 300calculates the first time (T1) based on the fixed time delay known tothe ECU 300 (Step 704). The calculated first time (T1) is a referencepoint at which the ABS data will be analyzed. The ECU 300 furthercalculates wheel phase angle (P1) by subtracting the wheel phase angledifference (PD) from the second phase angle (P2) (Step 706). The ECU 300retrieves historic ABS data that is stored and determines ABS trace atthe first and the second times (T1, T2) (Step 708). Subsequently, theECU 300 compares wheel phase angles (P1, P2) which are transmitted fromthe wheel unit against ABS data at the first and the second time (T1,T2) (Step 710). As a result, the ECU 300 assigns the identifier to alocation whose phase angle difference of ABS data mostly closely matchesto the wheel phase angle difference transmitted from the wheel unit(Step 712).

FIG. 8 is a flow chart further illustrating another embodiment of theauto-location method. In the illustrated embodiment, the wheel phaseangles (P1, P2) are received at the second time (T2) (Step 802), asshown in FIG. 8, unlike the embodiments illustrated in FIGS. 6 and 7.The ECU 300 calculates the first time (T1) based on the fixed time delayas the reference point (Step 804). Subsequently, the ECU 300 retrievesstored ABS data and determines ABS trace at the first and the secondtimes (T1, T2) (Step 806). The ECU 300 then compares wheel phase angles(P1, P2) which are transmitted from the wheel unit 101 against ABS dataat the first and the second time (T1, T2) (Step 808). As a result, theECU 300 assigns the identifier to location whose phase angle differenceof ABS data most closely matches to the wheel phase angle differencetransmitted from the wheel unit (Step 810).

As discussed in connection with the above-described embodiments, thewheel units 101, 102, 103, 104 measure the wheel phase angle of theassociated wheels LF, RF, LR and RR at two different times and determinethe relative phase angle difference. The relative phase angle differenceis transmitted to the ECU 300 at a later measurement time such that therelative phase angle difference is compared with similar informationextracted from the ABS system. The ECU 300 will receive RF messages fromthe wheel units 101, 102, 103, 104 including the phase angle differenceand compare the phase angle difference from the wheel units 101, 102,103, 104 with the ABS data from the ABS sensors 201, 202, 203, 204. TheECU 300 periodically receives the ABS data and stores a variable rollingwindow of the ABS data which covers the first time (T1) and the secondtime (T2). Thus, the ECU 300 may estimate, by interpolation of the RFmessage phase measurement, what the ABS data from each ABS sensor wouldhave been between the first time (T1) and the second time (T2) andsearches for a match from the ABS data for a wheel unit that has asimilar wheel angle. The purpose of the correlation is to determinewhich set of ABS data matches with the deduced phase angle of the wheelphase angle sensor 212.

In the above-described embodiments, the ECU 300 determines and uses as areference point the first and the second times T1, T2 in order toperform the auto-location. The ECU 300 calculates the first time basedon the second time T2 and the fixed time delay known to the ECU 300. TheECU 300 then determines ABS data that corresponds to the first and thesecond time T1 and T2. In other words, the above-described embodimentsrely upon the first time (T1) and the second time (T2) to define arelevant wheel phase angle and relevant ABS data for correlation. Bycomparing two different sets of data within the identical referencepoints, T1 and T2, accurate correlation may be obtained. Simple andaccurate implementation of correlation between the wheel phase angleinformation from the wheel units 101, 102, 103, 104 and the ABS data maybe obtained. Furthermore, the period between the first time (T1) and thesecond time (T2) may be easily variable to accommodate changingsituations and ensure the system accuracy requirements.

Moreover, as the wheel units 101, 102, 103, 104 may calculate anddetermine the phase angle difference, calculation burdens on the ECU 300may be reduced. Because a tire pressure monitoring system is atime-sensitive application, reduced calculation time by the ECU 300 mayincrease accuracy and efficiency of such systems.

In the above-described embodiments, auto-location for determining thelocation of TPM sensors is performed based on the fixed time delaybetween the phase angle measurements and the variable phase angledifference. In another embodiment, the auto-location may also berealized by the wheel units 101, 102, 103, 104 and the ECU 300 knowing afixed phase angle difference or a fixed phase delta which will occurbetween variable measurements times (TD=T2−T1). In other words, thephase delta is fixed, and the period between the first time (T1) and thesecond time (T2), i.e., T2−T1 is variable. Referring to FIG. 9, theembodiment where the phase delta is fixed and the time period (T2−T1) isvariable is explained in detail. When a wheel unit 102 decides toperform an auto-location event, the wheel unit 102 waits until itreaches a self-determined phase angle (P1). The wheel unit 102 thendetermines the time that the self-determined phase angle (P1) is reachedand stores such time (T1) (Step 902). In this embodiment, the wheel unit102 is discussed only for convenience and other wheel units 101, 103 and104 may be equally available. After rotating through the fixed phasedelta known to the wheel unit 102 and the ECU 300, the wheel unit 102reaches the second phase angle P2 (P2=P1+fixed phase delta) (Step 904).The wheel unit 102 determines the time that the second phase angle P2 isreached and stores the time (T2) (Step 904).

The wheel unit 102 transmits the identification, and Time Difference(TD=T2−T1) (Step 906). As discussed above in conjunction with FIG. 5,the wheel unit 102 transmits the same radio frequency message aplurality of times to ensure that the ECU 300 receives the radiofrequency message (Step 908). The ECU 300 receives the identificationand the Time Difference (TD). The ECU 300 correlates the Time Difference(TD) for a known phase angle with ABS information (Step 910). Theidentification is assigned to the ABS location which has swept throughthe fixed phase angle in the Time Difference (TD) (Step 912). In thisimplementation, the fixed phase angle does not have to be an integernumber of revolutions. In other words, the second phase angle (P2) doesnot have to equal (P1+(N*360°)), where N is an integer. The phasedifference (PD) could be encoded in the transmission at T2, or it couldbe a pre-determined value which is known to both the wheel unit and theECU.

The foregoing embodiments describe that the wheel unit transmits wheelphase angle information which includes actual measurements, a valuederived from the actual measurement, etc. such as first phase angle P1,the second phase angle P2, and/or the phase angel difference (PD). Thewheel phase angle information, however, is not limited to the actualmeasurement of the wheel phase angle and/or the phase angle difference.The wheel phase angle information may include any information indicativeof, and/or translatable to a wheel phase angle. Moreover, the wheelphase angle information may include information that prompts or triggersauto-location. For example, the wheel phase angle information mayinclude wheel phase angle indication. Receipt or detection of the wheelphase angle indication may trigger the ECU to perform a phasecorrelation data storage event. The ECU continuously maintains a rollingwindow of the ABS data. In response to the phase correlation datastorage event, the ECU stores or captures relevant ABS data. In oneembodiment, the wheel phase angle indication may include a predefinedfunction code. In another embodiment, the wheel phase angle indicationmay include setting a bit which is normally unused in a RF messagestructure, or a most significant bit of a certain data byte.Alternatively, or additionally, the wheel phase angle indication mayinclude temperature data or interframe spacings of RF transmissions.

Moreover, the foregoing embodiments compare a wheel phase angledifference with ABS data at two different times (T1, T2) to performauto-location of a wheel. Alternatively, or additionally, theauto-location of the wheel where the TPM sensor is arranged may requirea snapshot of information at one measurement point of a wheel phaseangle during a rotation of the wheel, where a snapshot is a capture ofinformation from a short duration of a continuous stream of information.The wheel unit transmits an RF message that includes or is associatedwith the wheel phase angle indication. The ECU holds a rolling window ofwheel phase and/or speed data such as ABS data for all wheels. Uponreceipt of the RF message, the ECU captures and stores a current contentof the rolling window of the ABS data. Then, the ECU determines relevantABS data from the rolling window at a predetermined time, i.e., T1. Anauto-location algorithm is applied to the stored ABS data in order toidentify the specific location of the wheel where the TPM sensor isarranged. Referring to FIGS. 10-17, these different embodiments of thewheel auto-location system and method are described below.

FIG. 10A illustrates the one-measurement point during the rotation ofthe wheel. The wheel unit 101 detects the first time (T1) when the wheelphase angle reaches the first phase angle (P1). The first phase angle(P1) is an angle of interest which may be set depending on the hardwareconfigurations of tire pressure monitoring systems. As one example, thefirst phase angle (P1) may be a zero-crossing point, i.e. zero, or apeak in order to facilitate efficient implementation of system hardwareconfigurations. The first phase angle (P1) is not limited to thezero-crossing point or the peak and any angle can be set as the firstphase angle (P1). The wheel unit 101 is described in this embodiment byway of example, and other wheel units 102, 103, 104 can be used. Thewheel unit 101 waits a predetermined time delay (TD=T2−T1) and transmitsa RF message. In this embodiment, the controller 202 of the wheel unit101 is programmed to know the predetermined time delay (TD). The wheelunit 101 may not measure a wheel phase angle at the second time (T2).Accordingly, the wheel phase angle at the second time (T2) isundetermined in this embodiment. In other embodiments, the wheel phaseangle at the second time (T2) may be measured. The ABS sensors 201, 202,203, 204 transmit ABS data to the ECU 300 via the receiver 400, asdescribed in connection with FIG. 1 above. In another embodiment, fewerthan four ABS sensors may transmit ABS data to the ECU 300, which willbe further described below.

FIG. 10B illustrates the rolling window of the ABS data from fourwheels. The ECU 300 continuously maintains the rolling window of the ABSdata as shown in FIG. 10B. The sinusoidal wave of the wheel phase angleat the first time (T1) and the second time (T2) is also shown in FIG.10B. The ECU 300 does not store or capture each rolling window of theABS data. Instead, the ECU 300 responds to a phase correlation datastorage event trigger and captures the current content of the rollingwindow of the ABS data that spans the first time (T1) and the secondtime (T2) as illustrated in FIG. 10B. The phase correlation data storageevent trigger will be described in detail below, referring to FIGS.11A-11D. The ECU 300 repeats this capturing or storing process multipletimes until a significant number of the current contents of the ABS datais captured and stored in order to ensure reliability.

FIGS. 11A-11D illustrate various embodiments of implementing the phasecorrelation data storage event trigger. FIGS. 11A-11D also illustratevarious embodiments of implementing wheel phase angle indication suchthat the phase correlation data storage event is triggered. FIGS.11A-11C illustrate contents of RF messages transmitted by a wheel unitand received by the ECU. Referring to FIGS. 11A and 11B, a firstembodiment of the wheel phase angle indication is explained. In thefirst embodiment, an RF message 1100 contains information correspondingto wheel phase angle indication. In FIGS. 11A and 11B, an exemplary RFmessage 1100 sent from the wheel unit 101 is illustrated. The RF messageincludes digital data arranged in a number of data fields including, forexample, a synchronization field such as a data preamble, a functioncode field, an identifier field, a pressure data field, a temperaturedata field and an error detection and correction field such as achecksum. Additional or fewer data fields maybe used and the fieldlocations in the RF message may be standardized to ensure reliablereception of the RF message. The structure of the RF message 1100 mayvary depending upon vehicle hardware and/or software where thisembodiment of the wheel auto-location system and method is used. In thisembodiment, the function code field corresponds to the wheel phase angleindication. The function code field may be referred to as a status codefield or a status byte field.

As described above, the wheel unit 101 transmits the RF message 1100 atthe second time (T2) after the wheel phase angle reaches the first phaseangle (P1) and waits the predetermined time delay (TD). The RF message1100 may not include an actual wheel phase angle, as shown in FIGS. 11Aand 11B. The RF message of FIG. 11A includes a preamble, a function code1110, an identification of a wheel, tire pressure, temperature, and achecksum. The RF message structure including the preamble, the tirepressure, the checksum, etc. as shown in FIG. 11A uses a conventional RFmessage structure. The function code 1110 may include a predefinedfunction code which prompts or instructs the ECU 300 to trigger a phasecorrelation data storage event. The phase correlation data storage eventindicates to the ECU 300 that a current content of a rolling window ofthe ABS data should be captured by the ECU 300. As described inconnection with FIG. 1 above, the ECU 300 receives ABS data from the ABSsensors 201, 202, 203, 204. The ECU 300 is continuously holding arolling window of the ABS data which has dimensions the same or greaterthan the predetermined time period (TD). As shown in FIG. 10B, the ECU300 captures the current content of the rolling window of the ABS datain response to the phase correlation data storage event and stores it inits storage.

Referring back to FIGS. 11A and 11B, the function code 1110 may includea bit that has been set or changed to set to trigger the phasecorrelation data storage event. As one example, the bit is normallyunused in a RF message structure. As another example, the bit includestwo most significant bits of a certain data byte, which is normally setto zero. As shown in FIG. 11A, the RF message 1100 sent from the wheelunit 101 includes wheel phase angle indication by adding the functioncode 1110. For example, the RF message 1100 is encoded to set a bit ofthe function code 1110 that triggers the phase correlation data storageevent. The RF message 1100 shown in FIG. 11A includes no actual phaseangle. The RF message 1100 may include the wheel phase angle indicationimplemented by the function code bits 1110. The structure of the RFmessage 1100 has benefits of including no wheel phase angle information.This message structure having no wheel phase angle information mayprovide flexibility as a standard frame protocol may not need to changein order to include phase angle information.

In FIG. 11B, the RF message 1100 may include data defining thepredetermined time delay (TD=T2−T1) 1120 using a dataframe assigned totemperature data in addition to the function code bits 1110. Thepredetermined time delay may represent the wheel phase angle. In anotherembodiment, the RF message 1100 may include a pseudo-random number thatindicates or is translatable to the wheel phase angle. Various types ofinformation which represents the wheel phase angle may be included inthe RF message 1100. For example, the wheel phase information could beencoded into 8 bits of data. This would allow a phase resolution of360/255=1.41° to be realized.

Another method to provide wheel phase information is to assign a code tospecific wheel phase angles. The transmitter 214 (FIG. 2) would thentransmit the code which corresponds to the particular phase angle ofinterest. In this embodiment, the ECU 300 stores a lookup table in thestorage 304. The lookup table maps the codes to actual phase angles, andthe ECU 300 then deduces the phase from the transmitted code. In afurther embodiment, the time delay (TD) may be one of several optionsknown to both the wheel units 101, 102, 103, 104 (FIGS. 1 and 2) and theECU 300. More specifically, the wheel units 101, 102, 103, 104 willtransmit a short code which corresponds to one of the several options.The ECU decodes the short code, and determines which of the severaloptions for the time delay (TD) have been used by the wheel units 101,102, 103, 104. In a further embodiment, the wheel units 101, 102, 103,104 may encode the actual time delay (TD) value in the radio frequencytransmission. For example, with a resolution of 1 millisecond and eightbits of information, a time delay of 255 milliseconds could becommunicated.

Referring to FIG. 11C, a second embodiment of the phase correlation datastorage event trigger is described. FIG. 11C illustrates an RF messagethat includes temperature data 1130. In this embodiment, the temperatedata 1130 includes 8 bits. As shown in FIG. 11C, 8 bits of temperaturedata indicate the normal operating temperature range of the tirepressure sensor 208 (FIG. 2). The normal operating temperature generallyranges from −40° C. to +125° C., and the temperature byte 1130 has thecapability to indicate temperatures from −50° C. to +205° C. Thetemperatures above +125° C. may not have any practical application.Accordingly, some of the temperature bits are used to encode the wheelphase angle indication. By using the example illustrated in FIG. 11C,the temperature of +142° C. corresponds to 11000000 and the two mostsignificant bits of the temperature byte are ‘11.’ The temperature of+142° C. is well above the maximum operating temperature. The code,11000000 may be used to trigger a phase correlation data storage eventin this embodiment.

In FIG. 11D, a third embodiment of a phase correlation data storageevent trigger is illustrated. In the third embodiment, an interframespacing among a series of RF message transmissions corresponds to thewheel phase angle indication and is used to trigger the phasecorrelation data storage event. In this embodiment, multiple RF messagetransmissions occur during the one second transmission. For instance,the identical information is transmitted eight times over a one secondtime period. The structure of the RF message frame, the number of RFmessage frames and the interframe spacings discussed in this embodimentare only by way of example and not limited thereto. The structure of theRF message frame, the number of RF message frames and/or the interframespacings may vary.

As shown in FIG. 11D, each interframe spacing between two consecutive RFtransmissions varies. In this embodiment, 109.86 ms, 189.94 ms and159.67 ms are respectively set as interframe spacings. The interframespacings are encoded and known to the ECU 300. When the ECU 300 receivesthe first three RF transmissions 1140, 1145 and 1150, the ECU 300recognizes the interframe spacings of 109.86 ms and 189.94 ms. Then, theECU 300 calculates when the first RF transmission 1140 is received. Thetime that the first RF transmission 1140 is received corresponds to thesecond time (T2). The ECU 300 subsequently calculates the first time(T1) and determines the ABS data at the first time (T1).

In FIGS. 11A-11D, various embodiments of the phase correlation datastorage event trigger are explained. However, the wheel auto-locationmethod is not limited to those embodiments and other ways ofimplementing the phase correlation data storage event are available. Asdescribed in connection with the embodiments of FIGS. 11A-11D, the ECU300 receives or recognizes the phase correlation data storage eventtrigger based on the wheel phase angle indication. The ECU 300 respondsto the wheel phase angle indication and performs the phase correlationdata storage event. As illustrated in FIG. 10B, the ECU 300 stores orcaptures the current content of the rolling window of the ABS data inresponse to the wheel phase angle indication. Then, the ECU 300calculates the first time (T1) based on the predetermined time delay(TD) which has been known to the ECU 300. The ECU 300 determinesrelevant ABS data from the ABS data stream, i.e., the stored currentcontent of the rolling window of the ABS data relevant to the first time(T1). In this embodiment, the relevant ABS data corresponds to an ABStooth count number at the first time (T1). The relevant ABS data isstored over time as the ECU 300 receives the RF message 1100 multipletimes and repeatedly determines and stores the relevant ABS data. TheECU 300 stores the ABS data in the storage 304 and executes anauto-location algorithm that correlates the stored relevant ABS datawith a specific wheel location. The auto-location algorithm is executedto identify the specific wheel location based on the trace of therelevant ABS data using a statistical correlation method.

Referring to FIG. 12, one embodiment of an auto-location method isfurther explained in detail. The wheel unit 101 detects the first phaseangle (P1) which is set as an angle of interest at the first time (T1)when the first phase angle (P1) is reached (Step 1210). The first phaseangle (P1) is not limited to a particular angle and is set depending onsystem hardware configuration. Actual values of the first phase angle(P1) may depend on a frequency of wheel rotation.

The wheel unit 101 waits for the predetermined time delay (TD=T2−T1)where the time delay is known to the ECU 300 (Step 1215). The wheel unit101 may not measure a phase angle other than the measurement at thefirst time (T1). In this embodiment, timing of one measurement, i.e., T1and the predetermined time delay (TD) may be indicative of the wheelphase angle. Actual phase angles of the wheel may not be used.

After waiting the predetermined time delay (TD), the wheel unit 101transmits the RF message 1100 to the ECU 300 at the second time (T2)(Step 1220). The RF message 1100 includes the wheel phase angleindication. As described above, the RF message 1100 includes predefinedfunction code bits 1110 such that the phase correlation data storageevent will be triggered by the ECU 300.

The ECU 300 continuously maintains a rolling window of the ABS data, thewindow having dimensions the same or greater than the predetermined timedelay (TD). The ECU 300 receives the RF message 1100 and recognizes thefunction code bits 1110 (Step 1225). When the RF message 1100 includesthe time delay (TD) data, the ECU 300 also recognizes such data. Whenthe time delay (TD) data is recognized, the ECU 300 stores the currentvalues in the rolling window of the ABS data. These current values ofthe rolling window will be used by the ECU 300 to perform the phasecorrelation data storage event upon receipt of the RF message 1100.

The ECU 300 calculates the first time (T1) based on the predeterminedtime delay (TD) upon receipt of the RF message 1100 (Step 1230). The ECU300 then determines an ABS tooth count for each wheel at the first time(T1) (Step 1235). The ECU 300 stores the ABS tooth count and repeatsthis process until a significant number of the phase correlation datastorage events have occurred (Step 1240). The stored ABS tooth countvalues are provided as an input to the auto-location algorithm. Theoutput of the auto-location algorithm is the association of a wheel unitID with a specific ABS sensor location on the vehicle.

Referring to FIGS. 13-17, the auto-location algorithm is explained.FIGS. 13 and 14 illustrate one example of the ABS tooth count values atthe first time (T1) for all wheels which have been stored by the ECU300. With respect to a series of the RF transmissions from a left rearwheel unit, the ABS tooth count values at the first time (T1) from aleft front ABS sensor are 93, 82, 18, 48, 71 for the first fivetransmissions. Likewise, the ABS tooth count values at the first time(T1) from a right front ABS sensor and a right rear ABS sensor are 40,23, 62, 47, 55 and 15, 57, 20, 4, 12, respectively, for the first fivetransmission. On the other hand, a left rear ABS sensor shows astatistically significant and consistent tooth count values, i.e., 32,30, 29, 30, 31 at the first time (T1) for the first five transmissions.Even after 15 transmissions, the consistent tooth count values remainunchanged. The auto-location algorithm uses the stored ABS tooth countvalues as an input.

The stored ABS tooth count values as shown in FIGS. 13 and 14 enable theECU 300 to perform statistical processing. The stored ABS tooth countvalues show a historic trace of the ABS tooth count values for eachwheel. By statistically processing the trace of the ABS tooth countvalues at a one-measurement point, identifying a specific location of awheel is achieved. One example of the statistical processing uses astandard deviation of the ABS tooth count values over time, as will bedescribed in detail below. Another example of the statistical processingmay include variance. The statistical calculation will also be designedwith consideration of ease of calculation and minimization of memoryresources.

Referring to FIGS. 15A and 15B, FIG. 15A illustrates one example of thestandard deviation for all four wheels, and FIG. 15B illustrates oneexample of the tooth count values for all four wheels with respect tothe RF transmissions from the left rear wheel. When the auto-locationalgorithm calculates the standard deviation, the wheel location isassociated with the location of the ABS sensor whose ABS data shows thelowest standard deviation (Step 1706). Referring to FIG. 16, thecorresponding ABS sensor indicates the lowest standard deviation of ABStooth count values.

In this embodiment, the auto-location algorithm determines a standarddeviation of a series of ABS sensor tooth count values. As shown in FIG.16, the ABS sensor assigned to a corresponding wheel shows a loweststandard deviation. For instance, for the left front (LF) wheel, theleft front ABS sensor shows the lowest standard deviation. In otherwords, the left front ABS sensor shows the most consistent tooth countvalue at the first time (T1). Also, the left front ABS sensor shows astatistically significant trend. Likewise, for the right front (RF)wheel, the right front ABS sensor shows the lowest standard deviationwith regard to a series of ABS tooth count values at the first time(T1). Thus, the ECU 300 executes the auto-location algorithm andcorrelates the ABS tooth count values with a specific wheel location. Asa result, the ECU 300 assigns a wheel unit ID to the specific wheellocation which is associated with the specific ABS sensor location.

FIG. 17 is a flowchart illustrating one embodiment of the auto-locationalgorithm. As a drive of a vehicle begins, the ECU 300 receives a RFtransmission including tire pressure and needs to identify the locationof a wheel associated with the RF transmission (Step 1702). The ECU 300checks whether a significant number of phase correlation data storageevents have occurred and a reliable database is formed. When thereliable database is formed, the ECU 300 activates the auto-locationalgorithm (Step 1702). By way of example only, full auto-location timesmay be less than 5 minutes, with an average of less than 2 minutes. Theauto-location algorithm remains active through the remainder of thatdrive. In this embodiment, the auto-location algorithm includesinstructions of retrieving stored ABS tooth count values at the firsttime (T1) for each wheel during N consecutive RF transmission from eachwheel (Step 1704). Referring to FIG. 13, ABS tooth count values, 93, 82,18, 48, 71 . . . are retrieved with respect to the left front wheel.Likewise, different ABS tooth count values at the first time (T1) areretrieved with respect to the right front, the right rear and the leftrear wheels.

In this embodiment, the auto-location algorithm further includescalculating a standard deviation of a series of ABS tooth count valuesfor each wheel (step 1706). Alternatively, or additionally, theauto-location algorithm further includes instructions of determining astatistically significant trend of ABS tooth count values for each wheel(step 1708). In another further embodiment, the auto-location algorithmincludes instruction of determining dynamic thresholds of a wheel unitassociated with the tooth count values of minimum deviation. Dynamicthresholds allow the wheel auto-location system to dynamically changethe decision parameters for the wheel assignment logic, i.e., the valueset for the standard deviation can be changed. In one embodiment,dynamic thresholds indicate a multiple of the minimum deviation. Theassociation decision will be based on the dynamic thresholds and thuswill react to adverse operating conditions. Adverse operating conditionsmay be present in situations where a vehicle experiences driving onrough roads, extreme braking, etc. It is also advantageous to permit thesystem to have flexible, self-determined threshold criteria whenoperating on a surface which is conducive for optimal accuracy of wheelphase angle determination, but which results in the vehicle wheel speedshaving minimal difference.

When the auto-location algorithm determines a statistically significanttrend of ABS tooth count values, the wheel location is associated withthe location of the ABS sensor whose ABS data shows the most consistenttooth count values or a statistically significant trend. Referring toFIG. 15B, the left rear ABS sensor shows the most consistent tooth countvalue and the lowest standard deviation at the first time (T1)throughout the series of RF transmission from the left rear wheel.

In the above-described embodiments, four ABS sensors are associated witheach of four wheels in the vehicle. In another embodiment, the vehicle'sABS system does not provide wheel phase and/or speed data for all wheelson the vehicle. FIG. 18 is a flowchart illustrating an embodiment wherefront wheels are associated with ABS sensors and the remaining wheelsare not associated with ABS sensors. Vehicle platforms may differdepending on vehicle models, manufacturers, vehicle designs, etc. Somevehicle platforms are installed with four ABS sensors at each wheel of avehicle, but other vehicle platforms may be equipped with fewer numbersof ABS sensors. In this embodiment, the ABS system provides informationfor the wheels on a front axle and does not provide information for thewheels on a rear axle. In that case, the ABS data for the wheels on thefront axle are correlated with the wheel phase angle indication from thewheel units mounted on the wheels on the front axle, as described indetail in the above-described embodiments. Accordingly, the ECUdetermines the location of TPM sensors arranged with the wheels on asingle axle.

The remaining wheels are not associated with ABS sensors as they arelocated on the other axle of the vehicle. With respect to the remainingwheels, the wheel units arranged on the remaining wheels can determineif the TPM sensor is arranged on the left or right hand side of thevehicle. For example, the wheel unit may compare phase signals from anaccelerometric device, or other mechanism in order to determine rotationdirection, lead/lag relationship, etc. as described in detail incommonly owned U.S. Pat. No. 6,204,758 to Wacker et al. and U.S. Pat.No. 7,367,227 to Stewart et al. of which disclosure is incorporatedherein by its entirety. These two patents explain that position on theleft or right of the vehicle can be discerned from the polarity of theacceleration data, indicating direction of acceleration and lead/lagrelationship associated with clockwise or counterclockwise rotation of awheel associated with a TPM sensor. Such determination is combined withdetermination of the front/rear location of the TPM sensor based on theABS data from the ABS sensor arranged on the single axle.

As illustrated in FIG. 18, the wheel unit provides TPM sensorparameters, a wheel ID and left/right side information (Step 1802). Withregard to two wheels where ABS sensors provide ABS data, the stored ABStooth count values at the first time (T1) is retrieved during Nconsecutive RF transmissions from front wheels (Step 1804) as describedabove in connection with FIG. 17. The statistical value of the standarddeviation of a series of the ABS tooth count values for the front wheelsis calculated (step 1806). Alternatively, or additionally, astatistically significant trend of ABS tooth count values is determined(step 1808). The wheel ID and the TPM sensor parameters are assigned tothe ABS sensor that shows the lowest standard deviation and based on theleft/right side information from the wheel unit (Step 1810).Alternatively, the wheel ID and the TPM sensor parameters are assignedto the ABS sensor that shows the most consistent values and based on theleft/right side information from the wheel unit (Step 1812). Thisembodiment of using the left/right determination from the wheel unit andthe front/rear determination from the ABS sensors may provideflexibility and increased adaptability in making and using the tirepressure monitoring system and methods, because various differentvehicle frames from different vehicle manufacturers can be accommodated.

In the above-described embodiment, auto-location of a TPM sensor is alsoperformed based on the snapshot of information at one measurement point(i.e., T1) during a rotation of the wheel when the time delay (TD=T2−T1)is fixed. The transmission time (i.e., T2) is used to calculate anddetermine the first time (T1) at the ECU 300. The ECU 300 determines therelevant ABS data at the first time (T1) from the rolling window of theABS data and stores the relevant ABS data. In one embodiment, therelevant ABS data includes ABS tooth count values at the first time(T1). The ECU 300 responds to the wheel phase angle indication includedin the RF message 1100 sent from the wheel unit 101. The wheel phaseangle indication may include function code bits set to trigger the phasecorrelation data storage event. In response to the function code bits,the ECU 300 captures the ABS data and determines the relevant ABS dataat the first time (T1). Once sufficient ABS data is captured and stored,the relevant ABS data is provided as the input to the auto-correlationalgorithm. The auto-correlation algorithm uses the statisticalcorrelation process that considers the standard deviation of orconsistency in ABS data traces. Then, the auto-correlation algorithmassociates the specific wheel location with the wheel location of theABS sensor whose ABS data shows the lowest standard deviation, or themost consistent ABS tooth count values and determines the location ofthe TPM sensor arranged with the specific wheel location.

In this embodiment, no actual wheel phase angle may be provided to theECU 300. Rather, the wheel phase angle indication, which may beimplemented with setting unused bits, using the function code or thetemperature data, setting interframe spacings, or any other availablemechanism, is provided to the ECU 300. Moreover, based on information atthe one-measurement point during the rotation, the auto-location of thewheel is achieved. Accordingly, the above-described the auto-locationsystems and methods may be simplified and produce fast output. Moreover,power consumption from the auto-location operation may be minimized.Also, the standard data frame protocol may be used as no actual wheelphase angle is included in the RF message data frame. Additionally, theabove-described auto-location systems and methods are applicable tovarious different vehicle frames where four or less ABS sensors areused. This may increase flexibility of the above-described system andmethods as specific ECU requirements may be removed and differentvehicle frames can be accommodated.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

We claim:
 1. A wheel auto-location method, comprising: receiving a radiofrequency (RF) transmission that indicates a one-measurement pointduring a rotation of a wheel and TPM sensor parameters, wherein the RFtransmission is associated with a phase correlation data storage eventtrigger; storing a current content of a rolling window of an antilockbrake system (“ABS”) data indicative of a wheel phase angle in responseto the phase correlation data storage event trigger, wherein a timeperiod covered by the rolling window is the same or greater than a timeperiod between the one-measurement point and a receipt point of the RFtransmission, and the current content of the rolling window correspondsto the ABS data between the one-measurement point and the receipt pointof the RF transmission; calculating the one-measurement point based onthe time period between the one-measurement point and the receipt pointof the RF transmission; determining relevant ABS data from the currentcontent of the rolling window of the ABS data based on theone-measurement point over time; and applying an auto-location algorithmto the relevant ABS data to identify a specific location of the wheelwhere the TPM sensor parameters are associated with the specificlocation of the wheel.